1. Field of the Invention
The present invention relates to a production process of a piston in the internal combustion engine, more particularly relates to a process for organizing composite structure of a portion in the vicinity of a ring groove where the piston ring is attached so as to improve the heat resistance and the abrasion resistance thereof.
2. Description of the Related Art
As such kind of production process of a piston, there is the one disclosed in Japanese Laid-Open Patent Publication No. Hei 2-125952.
In the art disclosed in Japanese Laid-Open Patent Publication No. Hei 2-125952, as shown in FIGS. 1A, 1B and 1C, a groove 13 is preliminarily formed on a portion which is an outer peripheral face 11a of a piston 11 comprising an aluminum alloy and where a ring groove 12 (see FIG. 1C) for attaching a piston ring is finally formed, and after a copper wire rod 14 is inserted and fitted to this groove 13, electron beam is irradiated thereto, thereby a melt diffusion layer 15 obtained as an aluminum-copper alloy layer is formed, then the melt diffusion layer 15 is subjected to the grooving process to form a ring groove 12 as shown in FIG. 1C.
According to the conventional method as described above, if the content of copper is increased for alloying with aluminum alloy which is a base material of the piston 11, a brittle intermetallic compound is formed between aluminum and copper. Therefore, the content of copper which is recognized to be more advantageous as it is increased, from the viewpoint of heat resistance and abrasion resistance, is limited to around 10 to 35%. Therefore, the matrix (base phase) of the melt diffusion layer 15 obtained as the aluminum-copper alloy layer as described above is basically aluminum-based, therefore cohesive abrasion is likely to be caused between the .alpha. phase and the piston ring made of cast iron, thus it has not necessarily been satisfactory from the viewpoint of abrasion resistance.